This invention relates to a method and an apparatus for producing a compilation of overlapping songs, each song in the compilation having a sequence of repeating beats. The compilation may, for instance, be suitable for recording onto a data carrier such as a compact disc, or for broadcast by a radio station.
It will be understood that by song we mean any musical song or tune, with or without a vocal element, and with or without elements of melody and harmony, where the rhythmic element of the music is characterised by repetitive beats. The invention is especially but not exclusively suitable for compilations of dance music, which is generally characterised by a continuous repetitive sequence of beats. The beat is important for dance music and usually dominates the overall subjective impression provided by the song.
It is well known to manually produce a compilation by xe2x80x9cmixingxe2x80x9d together a set of individual songs, usually dance music songs, to form a single continuous track in which one song is merged seamlessly into the adjacent song or songs. The resulting compilation comprises an apparently continuous stream of music.
At present, the production of such xe2x80x9ccompilationsxe2x80x9d (sometimes referred to as xe2x80x9cmixesxe2x80x9d) have required many hours work by skilled Disk Jockeys (DJ""s). The job of a DJ involves great skill in deciding on the order of the songs, (the xe2x80x9csequencexe2x80x9d) and also skill in seamlessly mixing one track into the other. The amount of time and skill needed puts the production of compilation mixes beyond the abilities of most listeners.
We are aware of European patent application No. EP 0932157A1. This document describes an apparatus and method for automatically performing a cross-over between two songs which are played back consecutively. As soon as the start of a pre-determined end part of the first song is detected, this end part is played simultaneously with a pre-determined beginning part of the second song. After play-back of the end part concludes, the play-back continues for the second song only. During simultaneous play-back a fade-out and/or a fade-in may be performed for the end part and/or the begin part respectively.
The apparatus known from EP 0932157 has problems in that it requires, as a pre-requisite, that two songs are provided which include markers for the end part and begin part. Most, if not all songs, can not be purchased with suitable markers allocated to them for use by such an apparatus. It is not taught how such markers are established, and presumably a skilled operator is needed in order to set the markers prior to play back and choose the sequence of the songs.
An object of the present invention is to produce a method and apparatus for the production of a compilation mix of songs which does not require the presence of pre-established markers and provides for greater flexibility.
According to the present invention, a method of automatically producing a compilation mix from a set of songs is provided, the method comprising the steps of:
(a) generating a beat profile comprising a temporal map representing an ideal rate of repeat of the dominant beat for the compilation mix at different points in time over the duration of the compilation;
(b) generating at least one set of song data indicative of the rate of repeat of the dominant beat for each of the songs in the set of songs,
(c) allocating the songs temporally within the compilation mix by processing the song data together with the temporal map, the songs being located temporally with respect to one another such that the rate of repeat of the dominant beat of the compilation approximates that of the temporal map and end portions of adjacent songs overlap.
The invention thus provides a method of automatically determining the sequence of the songs according to their rate of repeat of the dominant beat (the tempoxe2x80x94usually measured as beats per minute) and an ideal temporal map for the resulting compilation. This enables the production of effective compilations with a predetermined overall feel to be achieved from any set of songs.
The invention may include a preliminary step of selecting the set of songs to form the compilation mix from one or more master sets of songs.
The method step (a) may comprise the sub-steps of selecting a beat profile from a set of different predetermined beat profiles. The predetermined beat profiles may be stored within an area of memory.
The beat profile may comprise a quantitative map of the ideal beat repetition rate throughout the duration of the compilation to be constructed. It may comprise a set of beat rate values and corresponding time values for a compilation.
Alternatively, the temporal beat profile may be a qualitative map in which relative values of the beat repetition rate at various time locations in the compilation are provided. For instance, the map may consist of the location in time in the compilation of where the maximum and minimum rates should be, and the change in rate between these points.
The time information in the map may also be either quantitative, i.e. from zero to 74 minutes or qualitative, i.e. from xe2x80x9cstartxe2x80x9d to xe2x80x9cfinishxe2x80x9d.
The beat profile may be stored as a set of pairs of data, each pair consisting of a time location in the compilation and either a quantitative or qualitative value of the beat repetition rate.
The predetermined beat profiles may all be of a predetermined duration. In that case, the method may further comprise the steps of temporally expanding or compressing the selected profile to match the length of the compilation mix that is being produced.
The step of selecting the beat profile may be automatically performed by the method. A beat profile may, for example, be selected at random from a set of profiles.
Alternatively, the beat profile may be entered or selected manually by a user. The method may therefore include a sub-step of requesting a user to enter or to select a beat profile.
The step (b) of generating song data may comprise processing each song that is selected to produce a beat value representative of the rate of repetition of the dominant beat of the song.
Typically, the beat repetition rate (tempo) of a song will remain substantially constant over the duration of the song. The beat repetition data for each song may therefore comprise a step of, for each song, measuring the beats per minute of only one part of the song. This may, for instance, be a start portion, a middle portion or an end portion of the song.
It may also include the step of processing each song to produce a time value indicative of the overall duration of the song from start to finish.
It may additionally or alternatively include the step of identifying the location of any beat drop-outs within each song. These represent points in the song where the beat stops before restarting. For instance, in a dance music song it may be a point at which a drum beat defining the dominant beat stops for a few beats or measures before restarting.
The generated song data may be stored in individual data files corresponding to each song or in a single file.
The beat profile may be used to calculate the value and the temporal position of the minima and maxima beat rates in the profile. Data indicative of the value and position may be stored in a memory. In some arrangements, the temporal map may already be stored in terms of minima and maxima, and so this processing is not required.
The songs may be allocated to their temporal positions within the compilation such that the songs having the minima and maxima beat per minute are located at the point in the sequence corresponding approximately to the position of the minima and maxima of the temporal map.
The remaining songs may be allocated to the remaining positions in the compilation mix to complete the sequence by matching the beat rates of the songs to the temporal profile using a xe2x80x9cbest-fitxe2x80x9d approximation.
The allocation may be made by processing the song data in combination with the temporal map.
It is expected that in many applications of the present invention the duration of the created compilation will be required to be no greater than some maximum time-duration M seconds. For example, in creating a compilation to be written to a standard length compact disc (CD), the CD format imposes a maximum duration of 74 minutes (M=4440 seconds). In a broadcast application the compilation mix may have to fit into a precise time slot (i.e.12:05 to 1:00 am) and so the maximum time in this case would be 55 minutes.
To create a continuous/seamless mix, the songs in the compilation need to be overlapped so that the mix can cross-fade from one song to another. A variety of overlaps are envisaged within the scope of the present invention.
The method may therefore comprise the further step of, after allocating the songs to the temporal map to determine the order of the songs, locating the songs relative to one another in time such that the songs overlap in a predetermined manner.
The predetermined amount of overlap between songs may initially be chosen to be the same for each song.
For a set of N songs, with total combined length T seconds, the initial amount of overlap L between each song may be automatically determined from the relative values of M and T. If T is greater than M, there is more music than can be fitted into the time duration so each song may be overlapped by an equal amount determined by the equation:
L=(Txe2x88x92M)/(Nxe2x88x921).
Subsequent to the generation of the initial overlap, the individual overlap between pairs of songs may be adjusted. For example, where the song data indicates that a beat drop out is present in a song, this may be used as the point at which the song ends and the subsequent song begins. In that case, the decision to provide equal overlap may be overruled.
After initial overlap of the songs, the method may further comprise the step of processing the songs so that the beats occurring in the overlap section from each song are aligned temporally.
This step may comprise the step of phase aligning the overlapping songs so that the dominant beats of each song are exactly aligned. Thus, the beats of each song will occur at the same time and to the listener will appear as a single beat.
The dominant beats in the overlap can only be aligned throughout the entire overlap portion if they are at the same repetition rate.
The method may therefore include the step of time-stretch and/or time-compression processing one or both of the overlapping portions to match the rate of repetition. This may be achieved by speeding up one song in the overlap region, or slowing down one song, or a combination of both.
Where the method comprises the step of speeding up/slowing down an overlapping portion of a song, the method may further comprise the step of gradually adjusting the speed of the remainder of the song over time to bring it back to its nominal (pre-adjusted) beat repetition rate. The human ear is not especially good at identifying slow changes in tempo over time, and so such adjustment can be made without the user noticing in the final compilation.
After the songs have been aligned the subsequent alterations to the overlaps may require that the overall length of the resulting compilation exceeds the allocated duration, i.e. exceeds M seconds. In such a case, the method may further comprise the step of automatically truncating the compilation by fading out the final song early (before its end) or fading in the first song late (after its start), or by a combination of both.
The same step of early/late fade can also be applied if the duration of any one of the calculated overlaps exceeds a predetermined value L. This can arise if the overlap is aligned using a drop-out that occurs some way into a song. The value of L may be quantitative, i.e. 30 seconds, or qualitative, i.e. 30 percent of the duration of a song. Thus, if the overlap exceeds the predetermined threshold an appropriate fade-out, fade-in or both may be used to lower the overlap to within the threshold.
If no maximum time limit is set, the overlap may be chosen at random or set to some predetermined initial value, say 20 seconds. This may also be used where the total length T of the songs for the compilation are less than the predetermined limit M. The value of the overlap may be selected as a function of the length of the songs being compiled, for example as a percentage of the length of an outgoing song, as a percentage of a length of an incoming song, or as a percentage of the average length of the songs being overlapped. This percentage could be fixed or generated at random from a probability distribution.
The method may further include the step of fading out the amplitude (volume) of the overlapping end portion of a song. The method may also include the step of fading in the overlapping start portion of a song. A linear increase in amplitude may be provided or it may be faded in accordance with any other predetermined pattern.
The method may further comprise the step of recording the songs in their selected order over time onto a data carrier, such as a compact disc.
According to a second aspect, the invention also provides apparatus adapted to automatically produce a compilation mix of songs in accordance with the method of the first aspect.
The apparatus may include a first area of memory in which the songs to be compiled are stored, a processing unit which processes the data in the memory, a computer program which, when run on the processor instructs the processor to perform the method of the first aspect of the invention.
A second area of memory may be provided in which one or more user defined beat profiles are stored for access by the processor.
The apparatus may further include a connector for connection to an output storage device adapted to record the resulting compilation on a storage data carrier. The storage device may comprise a compact disc writer.
The apparatus may include a data input device whereby a user may select the temporal profile in response to a prompt by the apparatus. The apparatus may produce an audio or visual prompt.
According to a third aspect, the invention provides a data carrier including a computer program which, when operating on a computer, produces an apparatus according to the second aspect of the invention.